Sightings

Sightings

NASA's J-Pass can track satellites from almost any
backyard.

May 6, 1999 : If you've
ever wished upon a falling star, you may have actually pinned
your hopes on a piece of machinery. There are over eight thousand
manmade satellites orbiting our Earth every day. Because satellites
reflect sunlight back down to Earth as they pass overhead, they
often look like slow-moving stars.

Above: The lighter blue area is where
the Space Station can be seen from the ground.

A typical satellite in low Earth orbit (LEO)
circles the Earth sixteen times each day, traveling 7.5 kilometers
per second (27,000 km/hour). The best time to catch a glimpse
of a satellite is either at dusk or at dawn, because satellites
are most visible when they are in sunlight while the viewer is
in darkness.

Left: Patrick Meyer, author of JPASS, and its sister
program JTRACK, describes the program and how to use it. Click
on the image to view a RealVideo movie. (Go to RealNetworks
for a free player, if you need it.)

The brightest satellites also happen to be some
of the most famous: the new International Space Station, Russia's
Mir Space Station and the Space Shuttle, when in flight. These
larger satellites have been observed to be brighter than -1.0
visual magnitude. That is nearly as bright as Sirius (Alpha Canis
Major), the brightest star in the sky.

The trick to identifying these satellites is knowing exactly
when and where to look. Using NASA's Liftoff to Space Exploration
web site, you can find out which satellites will be passing over
your hometown.

All the lonely objects, where do they all come from?

Liftoff's
Java program, called J-Pass (at right), uses information provided
by the North American Strategic Defense Command (NORAD) for more
than a hundred bright satellites. NORAD keeps track of the more
than eight thousand objects traveling above the Earth. Over 2,500
of these objects are man-made satellites, both operative and
inoperative. Other satellites orbiting the Earth are actually
debris: nosecone shrouds, lenses, hatch covers, rocket bodies,
boosters, payloads that have disintegrated or exploded, and even
objects that have escaped during manned spacecraft missions.

Left: J-Track
3D shows 500 satellites orbiting the Earth.

Accessing J-Pass only requires a recent version of either
Netscape Navigator or Microsoft's Internet Explorer. J-Pass gives
satellite rise and set times for your location, and indicates
the part of the satellite pass that will be visible. The chart
even includes positions of visible planets and bright stars.
Sky charts can be printed out to be used as an outdoor reference
guide. For viewers without a Java ready browser, the Liftoff
site also has a mailing list system. By subscribing to the list,
viewers will be notified by e-mail of upcoming satellite passes.

Left: The animation at left shows a simulated
pass of International Space Station through the constellation
Orion. This is what a bright satellite pass is like. Visible
satellite passes occur after sunset and before dawn. JPASS will
also tell you the expected brightness of the satellite as it
passes overhead (negative numbers are brighter!).